请教一个小问题

pipilovelail

As is the case with traditional pharmacies, prescriptions are the cornerstone of a successful
on-line drugstore, since it is primarily prescriptions that attract the customers, who then also buy other health-related items.

since后面的it是指代谁啊，后面那个it is primarily prescriptions that。。。这里没读懂，帮忙翻译下 谢谢！

kray003

在用处方药赢得顾客的同时，顾客也会购买其他保健品。

it = prescriptions

sayysong

窃以为it是形式主语，指代的是后面的 that attract the customers
起初吸引顾客的是处方药，之后他们也会买些其他保健品。

kray003

呵呵，同意楼上，写完发现错了，没有再改。。

zjqswmm

it is primarily prescriptions that attract the customers
这是强调句哦~~~
It is 加要强调的部分加that再加其他句子成分

pipilovelail

再看我也觉得是强调句，谢谢楼上几位，我觉得很肯定，因为去掉it is primarily还有that，句子主谓宾全齐，顺序正常，这正是强调句的形式啊 哈 没想到那去。如果要是形式主语的话就是attract the customer is prescription，这显然不对啊！所以还是强调句正确哈哈

edward在奋斗

但是这里primarily作什么成分呢？修饰attract吗？GMAT里面副词修饰动词应该紧跟着所修饰名词吧？